Vacuum tube and associated element



Nov, 6, 1928.

W. H. T; HOLDEN VACUUM TUBE AND ASSOCIATED ELEMENT Original Filed June l, 1926 LTT E W1 CHM-f1( Mii- 1-l |l lI- indicates pfad batteries.

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WEZ'Ioldelz/ BY (i A TTORNEY Patented Nov. 6,1928.

WILLIAM H. T. HOLDEN, OF BROOKLYN, NEW YORK, ASSIGNOR TO- AMERICAN TELE- 'PATENT olii-*ica*l PHONE AND TELEGRAPH COMPANY, A CORPORATION F NEW YORK.

vAcUM TUBE AND ASSOCIATED LEMENT;

originaiapplimion iued :une 1, met, serial mi.- 11a,o2o. Divided and this application iuedAprii 2s,

1927.' SerialiNo.' 186,784.

i My invention relates to the amplification of electricA currents, and more particularly to the amplification of very small dlrect curtion with efforts to produce these vary small, y direct currents. TheseV difficulties are due to the fact that in the ordinary vacuum tube amplifier, even one having the best commercial -.vacuum, there is a minute vflowin to the grid, which current results from e ionization of the residual gas in the tube'bythe electrons constituting the space current. This current is ordinarily of a value from 10' to 1 0*a amperes. If direct currents of 4this m 'tude orsmaller are to befamplified, or i input resistances ofv I0 to v10la megohms are employed, the positive ioncur.- 3o rent to `the may cause difficulty b mask- `ing the direct current to be amplifie IThis positive ion current tothe grid may also alter the grid bias and, in addition, the character of the current is, in .all probability, unsteady. as For a discussion of ionization in vacuum tubes, reference may be badje/Vander Bijl,

Thermionic Vacuum Tube Chapter It is suilicient to state here a few points direct-- ly connected with the invention. When a i7 vacuum tube is used as an amplifier, most ofthe ionization of the gas (of whichv there is y (always a residuum) takes place between the and the anodeV or plate. Since the grid 1s lnegative with respect to the plate, the posi- A6. tive ions formed by collisionionization in this region are attractedY to the grid., The ionization energy of any gas or. vapor is the sma1lrest ener with'l which an electron must collide wi atom of that'gas or. vapor in l0 order completely to detach anlelectron therefrom. This amount of energy i`s usually ex pressed in terms of the voltage through which 1 the electron drops before it collideswith the atom and is then referred .to as the ionizasitive ion current cordingly, it has been proposed to eliminate I thesource of the difiiculty discussed above in amplifying minute direct currents by re- .ducing the plate voltage below this certain amount. This step alone, however, isprobably insuiiicient. Electrons having energies I sucient to excite resonance radiationfrom the atoms of4 the residual gas may give 'riseto-u grid current. The production of soft X-,rays occurring when the electrons strike'the plate may also result in grid4 current. This grid'- 'current is 'due to the emission of photo-electrons from the grid material as a result of the-- resonance or soft X-ray radiation to which the material is exposed. In other words, the

`residual gas in a vacuum tube has notI only 'an ionization voltage, 'which will give rise to -d current unless the plate voltage supplied 1s very low, but also a resonance voltage'some# v`what lower than the ionization voltage, which may result in ,plained above.

id "current, vas exthe approximate ionization and resonance voltages of mercury vapor and hydrogen:

I Ionilzatlon Resonance Sllbtm voltage voltage Mercury vapor-...`...;....I... c. 10.4 '4.9. Hydrogen 1-... i 9` Accordingly, if the ordinary t pe of .three-yl electrode vacuum tube .isused or the ampli- The ollowing table gives yficat.ion"o'l:' small direct currents, say,of 10"" amperes the plate voltage supplied to the tube must be reduced toa vlue from'7 toY 9 volts in order to'obtain a suliciently` close" approximation to the elimination cfg-rid curnary controlling grid andvanadditional grid y l called aspacecharge between the control gri l is positivelyy biased. By means of the addi. tion of this space l charge '(1,' a material increase in gain from thetu e may be obtained.

grid, which is placed nd the filament and f 5 AIt is the purpose of `this'invention to proi f vide means for permitting the use of a materiall higher plate voltage in a vacuum tube amp ifying system without the production of ionization or resonance radiation dilliculties..

I accomplish this object by employing in the amplifying system a vacuum tube treated in a novel and highly advantageous manner, the method being described below.

The nature and purpose of my invention will A be more clearly understoo when the following detailed description o the circuit, including a description of the preparation of my special tube, is read with reference to the accompanying drawing, which shows the circuits of the amplifying system in diagrammatic form The tubes V1 and V2 are connected in eascade. The tube V, is a double grid tube, while the tube V2 is of the ordinary three-electrode type. The biasing voltage for the control grld of the tube V1 is supplied from the source 2, and the voltage for the space charge grid l is supplied from the source 3, this grid being biased positively with respect to the control grid. The source 4 vsupplies the plate voltage for tube V1. The usual resistance R1 and R2 are included. Let it be assumed that a very small direct current z', is supplied tothe input of the system and that it is desired to amplify this current in order to produce a satisfactory operation of the meter M, which is connected in the plate circuit of the tube V2. A current is, considerably larger than the current il, must be produced in the plate circuit of tube V2, and, in order to obtain the proper value for this current, there must be produced in the plate circuit of the tube V1 a current 2, which, of course, must represent a large amplification of the input current il.

The tube V1, which is the double grid tube, is, according to my invention, speclally prepared to be suitable as an amplifier of the very small current il. It is known that helium has a relatively large ionization voltage and a correspondingly large resonance voltage, these bemg perhaps larger than the corresponding voltages of any other known gas or vapor. More specifically, the ionization voltage of helium is 29 volts, and its resonance voltage approaches 20 volts. In accordance with my invention, I subject the tube V1 to the well known exhaust and heat treatment. Bi this treatment, durin the exhaust, or, in ot er Words, while the tu e is on the molecular pump, a large current is passed through the filament in order to produce a temperature materially higher than that at which the tube is to operate in service. It is readily understood that the result of this heating of the filament isa severe electron bombardment of the anode and the grids. In accordance with my invention, upon the completion of the exhaust and heat treatment, lhelium is admitted to the tube. After a brief period of time, the

exhaust and heat treatment is repeated. In other words, the tube is flushed with helium. It may be desirable to repeat the Whole process several times. The result or this treat# ment of the vacuum tube is that the residual gases ordinarily present in an evacuated bulb, which gases have relatively low ionization and resonance voltages, are replaced or, at least, substantially replaced by helium, which has relatively high ionization and resonance potentials. In addition, helium has the advantage thatl it offers very little impedance to the passage through it of a stream of electrons at velocities below its resonance voltage. Relatively high pressures of helium ma therefore be left in the tube without dis vantage.

In order to secure the best operation of my amplifying system, the sum of the voltages from the sources 2, 3 and 4 should be less than the resonance voltage of the residual gas in the tube V1, that is, less than approximately 20 volts, or the resonance voltage of helium. The scope of my invention is defined in the appended claims.

I claim:

l. In a system for amplifying electric currents, a `vacuum tube and sources of anode and grid potentials therefor, said tube being iushed with a gas of a high resonance volt- 9B age, and the sum of the voltages from said sources being less than the resonance voltage of said gas.

2. In a system for amplifying electric currents, a vacuum tube having a cathode, an anode, a controlling grid, and a space charge grid, and a source of potential for each of said electrodes, said tube bein fiushed with a gas of a high resonance vo tage, and the sumof the voltages from the anode, controlim ling id, and space charge grid sources being less t an the resonance voltage of said gas.. 3. In a systemfor amplifying electric currents, a vacuum tube and sources of anode and grid potentials therefor, said tube hav- 11o ing a gaseous residuum composed exclusively of a gas 0f a high resonance voltage, and the sum of the voltages from said sources being less than the resonance voltage of said gas.

4. In a system for amplifying electric currents, va vacuum tube having a cathode, an anode, a controlling grid, and a space charge grid, and a source of potential for each of said electrodes, said tube having a gaseous residuum composed exclusively of a gas 'of a high resonance voltage, and the sum of the voltages from the anode, control.- ling grid, and space charge grid sources being less than the resonance voltage of said gas. 5. A vacuum tube and sources of anode and grid potentials therefor, said tube having a gaseous residuum composed exclusively of a gas of ahigh resonance voltage, and the sum of the voltages from said sources being less the voltages from the anode,el controlling than the resonanoe'voltage of said gas. grid, and space charge grid sources being less 10 6. A vacuum tube having a. cathode, an than the resonance voltage of said gas. l

anode, a controlling grid, and a s charge In testimony whereof, I have s1 ed m}f' ,5 grid,.and a source. of tential or each' of name to thisspecication this 23r 'day o said electrodes, said tu having a gaseous April, 1927. residuum composed exclusively of a gas of a high resonance voltage, and the sum of WILLIAM H. T. HOLDEN. 

